Please read this (which was written in regards to the Linux beta); this will give you an idea of what makes a good application, then drop an email to betatests@icculus.org telling your hardware/software config and why you'd make a good beta tester.

We're doing this test relatively quickly, so expect to spend some seriously intense time crunching on the game in the next week or so.

SCI will be
running forums for the testers and handling the boring stuff for me.

UPDATE: Mail sent here will eventually end up in the same place as the "betatester@supercomputerinc.com" email address that Bacchus posted on insidemacgames.com. So either address is fine.